An erc20 token has been smart contracted in MyEtherWallet(Ropsten) and verified & published in etherscan.io. I want to list this token in an exchange I've built. Can I do it by installing a private blockchain(geth) in my exchange server and able to do rpc calls like it's done for ETH? If it is not possible, what are the other options?

Can I do real-time trades on testnet instance?
– krkJul 16 '18 at 17:47

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Http-rpc is request-reply, for asynchronous events you need websocket protocol. You can do trades using your local instance, provided you use a funded account and specify some gas amount. Only funded transactions get propagated through the network, also in a testnet.
– rustyxJul 16 '18 at 17:52

I read that testnets are for only testing purpose. Does a testnet become mainnet if we apply gas price for it? If that is true, is it applicable for only erc20-tokens?
– krkJul 17 '18 at 6:10

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A testnet is like a mainnet except its ether is worthless. Instead of mining testnet ether, the testnet gives it out for free to anyone interested. The main principle of paying for gas though is still the same. A testnet never becomes mainnet.
– rustyxJul 17 '18 at 6:48